1. Field of the Invention
This invention generally relates to an electric circuit breaker and switch, and more particularly to a movable contact assembly for use in circuit breakers and switches.
2. Description of the Prior Art
Electrical circuit breakers of the type commonly referred to include a plurality of movable contact arms, each including a rigid contact arm and an elongated contact member having movable contacts pivotally supported on the contact arm. In these devices spring means are provided between the elongated contact member and the contact arm to limit the movement of the elongated contact member away from the rigid contact arm. Such electric circuit breakers are illustrated in Japanese utility model No. 976762 to M. Iida published on Feb. 28, 1972, and in U.S. Pat. No. 3,134,878 to C. L. Jencks issued on May 26, 1964, and U.S. Pat. No. 3,134,880 to F. H. Murphy issued on May 26, 1964.
In the above mentioned Japanese utility model specification, a pair of openings are provided within an elongated contact member to support a pin by a U-shaped supporting member. Similarly, in the device disclosed in both U.S. patent specifications, a pair of openings are provided therein. However, since the cross section of the elongated contact member is reduced due to the various openings, the current capacity of the elongated contact member is restricted. Furthermore, since the elongated contact member is repeatedly moved or operated, adequate mechanical strength of the elongated contact member is required.
In accordance with the teachings of these prior art references, in order to satisfy the condition of adequate circuit capacity and mechanical strength as discussed above, the structure of the prior art electric circuit breaker device requires a great deal of space. Furthermore, since the elongated contact member is surrounded by a movable contact arm and a pivot pin, i.e. a shorting ring, an eddy current flows in the shorting ring when a current flows in the elongated contact member thereby heating the shorting ring. In order to prevent heating generated by the eddy current and to prevent humming or buzzing produced in the shorting ring when the circuit breaker operates, the use of non-magnetic material as the pivot pin is required. As the result, the circuit breaker becomes expensive and the circuit breaker as a whole requires a great deal of space. Moreover, since the elongated contact member is usually made of copper material, it is affected by the eddy current when the circuit breaker is thrown and by mechanical shock when the circuit breaker is tripped. As the result, deformation of the elongated contact member occurs.